Electrocatalysts, the preparation thereof, and using the same for fuel cells

Abstract

Compositions comprised of a tin film, coated by a shell of less than 50 nm thick made of palladium and tin in a molar ratio ranging from 1:4 to 3:1, respectively, are disclosed. Uses of the compositions as an electro-catalyst e.g., in a fuel cell, and particularly for the oxidation of various materials are also disclosed.

What is claimed is: 
     
       1. A composition, comprising a metal core coated by a shell, wherein said shell:
 (a) comprises palladium (Pd) and tin (Sn), wherein the Pd:Sn molar ratio is in the range of 1:4 to 3:1, respectively; and 
 (b) is characterized by a thickness of less than 50 nm; and wherein the metal core comprises Sn, tin oxide, or both. 
 
     
     
       2. The composition of  claim 1 , wherein said metal core is in a form of a nanoparticle, a dendritic structure, or a film. 
     
     
       3. The composition of  claim 1 , wherein said shell further comprises a platinum (Pt). 
     
     
       4. The composition of  claim 3 , wherein said Pt and said Sn are present in the shell in a molar ratio of 2:1 to 1:1, respectively. 
     
     
       5. The composition of  claim 1 , wherein the shell is characterized by a thickness in the range of 2 nm to 10 nm; and wherein the shell is in a form of crystals having a median crystallite size in the range of 3.5 to 6 nm. 
     
     
       6. The composition of  claim 3 , characterized by an X-Ray Powder Diffraction which is devoid of peaks at positions that correspond to a pristine oxide of at least one element selected from Pt, Pd, and Sn. 
     
     
       7. The composition of  claim 1 , wherein said metal core is deposited on a substrate. 
     
     
       8. The composition of  claim 7 , wherein said substrate is selected from a carbon substrate, a metal oxide, a polymer, or any combination thereof. 
     
     
       9. The composition of  claim 7 , wherein said substrate is the carbon substrate selected from the group consisting of activated carbon, graphite, carbon nanotube, and nano-diamond, or any combination thereof. 
     
     
       10. The composition of  claim 7 , wherein said substrate is in the form of plurality of nanoparticles (NPs), wherein said plurality of NPs is characterized by a median size of from about 1 to about 50 nanometers. 
     
     
       11. The composition of  claim 1 , wherein said Pd:Sn molar ratio is from 3:4 to 1:4. 
     
     
       12. The composition of  claim 1 , being an electro-catalyst. 
     
     
       13. The composition of  claim 3 , characterized by a specific activity of at least 0.05 mA cm −2  Pt. 
     
     
       14. The composition of  claim 12 , wherein the electro-catalyst is capable of promoting a hydrogen oxidation reaction (HOR) with an onset potential of between about 0 mV in alkaline media. 
     
     
       15. The composition of  claim 14 , wherein the electro-catalyst is present in an anode of a fuel cell. 
     
     
       16. A hydrogen generator device comprising the composition of  claim 1 , configured to oxidize at least one material selected from the group consisting of methanol, ethanol, formic acid, formaldehyde, dimethyl ether, methyl formate, or any derivative thereof, and of reducing protons, forming a hydrogen. 
     
     
       17. A process for manufacturing the composition of  claim 1  comprising the steps of:
 (i) providing the metal core comprising tin (Sn), tin oxide, or both; and 
 (ii) depositing an alloy comprising Pd and Sn on said metal core, wherein Pd:Sn molar ratio within said alloy is in a range of 1:4 to 3:1, thereby obtaining said composition. 
 
     
     
       18. The process of  claim 17 , wherein the Sn core is in a form of a nanoparticle supported on the substrate. 
     
     
       19. The process of  claim 17 , wherein said depositing is by a process selected from electro-deposition, electroless deposition, sputtering, chemical vapor deposition, ion beam enhanced deposition, plasma-assisted vapor deposition, cathodic arc deposition, and ion implantation. 
     
     
       20. The process of  claim 17 , wherein said alloy further comprises Pt.